Video projection system

ABSTRACT

A video projection system ( 50 ) comprises a rotary disc ( 31 ) having light guiding devices ( 35 ) extending radially thereof and in a helical configuration circumferentially at the disc ( 31 ) and corresponding in number to the number of lines to be scanned on a screen ( 48 ) the arrangement being such that, as the disc ( 31 ) rotates, a light bundle is directed through successive devices ( 35 ) which cause the bundle to be scanned on the screen ( 48 ).

[0001] This invention relates to a video projection system.

[0002] In WO 95/03675 there is disclosed a video projection systemcomprising means for generating a colour light bundle coloured accordingto a video signal and means for line scanning the bundle onto a screenthereby producing images on the screen.

[0003] The system includes a disc which is adapted to rotate on an axisextending through a centre of the disc and at right angles to the planeof the disc, the disc having a series of plane mirror facets extendingcircumferentially of the disc on a circumferential surface thereof, anda plane mirror adapted to pivot relative to an axis extending throughthe plane of the mirror and parallel to a diameter of the disc forreceiving the bundle of light reflected from successive mirror facetsduring rotation of the disc.

[0004] A problem with such a known video projection system is that thefunctions required of the pivotable plane mirror are very demanding andare not achievable with today's technology and are unlikely to beachieved in the near future.

[0005] The present invention is characterised in that a video projectionsystem includes a disc carrying a plurality of light guiding devicesextending radially of the disc and spaced one from another in an angulardirection in the plane of the disc and each device extending at an angleto the plane of the disc in a corresponding plane perpendicular to theplane of the disc so that each device projects a corresponding one ofthe lines scanning a video image on to the screen.

[0006] In the video projection system in accordance with the presentinvention there is no requirement for a pivotable plane mirror.

[0007] Following is a description, by way of example only and withreference to the accompanying drawings, of one method of carrying theinvention into effect.

[0008] In the drawings:

[0009]FIG. 1 is a diagrammatic elevation demonstrating the concept of avideo projection system in accordance with the present invention,

[0010]FIG. 2 is a diagrammatic perspective view of the arrangement shownin FIG. 1,

[0011]FIG. 3 is a diagrammatic elevation of a preferred embodiment of avideo projection system in accordance with the present invention,

[0012]FIG. 4 is a diagrammatic perspective view of the embodiment shownin FIG. 3,

[0013]FIG. 5 is a diagrammatic elevation of another embodiment of avideo projection system in accordance with the present invention,

[0014]FIG. 6 is a diagrammatic perspective view of the embodiment shownin FIG. 5,

[0015]FIG. 7 is a diagrammatic elevation of another embodiment of avideo projection system in accordance with the present invention, and

[0016]FIG. 8 is a diagrammatic perspective view of the embodiment shownin FIG. 7.

[0017] Referring now to FIGS. 1 and 2 of the drawings, which arediagrammatic conceptual representations, a video projection system 10 inaccordance with the present invention comprises a disc 11 which isadapted to rotate on an axis 12 extending through a centre of the disc11 and at right angles of the plane of the disc. In this regard, thedisc 11 is secured on a shaft 13 of a motor 14, the central longitudinalaxis of the shaft 13 being coaxial with the axis 12. The disc 11 hasmounted thereon a plurality of light guiding devices 15 extendingradially of the disc 11 in a margin extending circumferentially of thedisc 11. The devices 15 are arranged in groups 16 and the devices 15 ineach group 16 are stacked one above another in respective radial planesof the disc 11 and extend at specified angles relative to the plane ofthe disc 11 in the respective planes. The planes containing the groups16 are angular spaced equidistant one from another throughout a 360degrees sweep of the plane of the disc 11.

[0018] The system 10 includes a plurality of component groups 17 eachcomprising three laser light sources 18, 19 and 20 for providingrespectively the colours red, green and blue of a video signal,corresponding modulators 21, 22 and 23 for modulating the intensity ofthe light bundles which issue from the light sources 18 to 20, a planemirror 24 and two plane dichroic mirrors 25 and 26 for combining into asingle light bundle, the modulated light bundles and a mirror 27 forreflecting the combined light bundles. The array of mirrors 27corresponding to the respective component groups 17 are stacked at alocation relative to the disc 11 spaced inwardly of the margin of thedisc 11 containing the groups 16 of light guiding devices.

[0019] The system 10 also includes an optical system, shown generally at28, for enlarging the horizontal projection angle, the optical system 28being located opposite the array of mirrors 27 and adjacent theperiphery of the disc 11, and a screen 29.

[0020] The system 10 may be adapted for scanning 625 lines on the screen28 for each {fraction (1/25)} of a second, where 25 is the number ofimages per second contained in the video signal. In order to achievethis, 125 groups 16 each comprising 5 light guiding devices 15 arelocated on the disc 11 (although only 25 groups 16 are shown in FIG. 2for clarity), each group 16 being positioned at an angle of 2.88 degreesin the plane of the disc 11 from an adjacent group 16 and the angularpositioning of the devices 15 in their respective radial planes relativeto the plane of the disc 11 is calculated so as to project light at anangle relative to the plane of the disc 11 according to the formula:—${+ 9} - {\left( {N - 1} \right) \times \frac{18}{624}{{degrees}.}}$

[0021] where N is the number positioning of a light guiding device 15 inthe range 1 to 625 starting from an uppermost guide 15.

[0022] The light guiding devices 15 each of which may be a light rod, awaveguide, a cavity, a lens or any combination thereof, in effect,provide a helical formation of 625 devices 15 during 5 consecutiverevolutions of the disc 11. The speed of the motor 14 is 125 revolutionsper second.

[0023] Since there are 5 light guiding devices 15 in each group 16,there are 5 component groups 17, each associated with a correspondingone of the 5 devices 15 of each group 16. The component groups 17control operation of the light guiding devices 15 as each of the devices15 moves between the mirrors 27 and the optical system 28, signalsswitching from one group 17 to another after each revolution of the disc11 until five revolutions of the disc 11 have been completed, when thesequence is repeated.

[0024] It will be appreciated that instead of there being 5 componentgroups 17, only one component group 17 may be provided which woulddirect the combined light bundle to the appropriate layer of lightguiding devices 15.

[0025] Referring now to FIGS. 3 and 4 of the drawings, there is shown apreferred embodiment of a video projection system 30 comprising a disc31 which is rotatable, on an axis 32 extending through a centre thereof,by means of a motor 33. The disc 31 is provided with a circumferentialmargin 34 of increased cross sectional dimension and the margin 34 isprovided with 625 light guiding devices 35 in the form of cavitiesenveloped in a laser reflecting material, each being curved in a planeperpendicular to the plane of the disc so as to project light at anangle in accordance with the formula stated above, each extendingradially of the disc 31 and each extending at an angle of 0.576 degreesone to another in the plane of the disc 31. The angular relationship ofthe light guiding devices 35 one to another in their respective planesperpendicular to the plane of the disc 31 is such that the sweep of thedevices 35 through 360 degrees of the circumference of the disc 31 ishelical in configuration.

[0026] The system 30 includes a component group 36 comprising threelaser light sources 37, 38 and 39 for providing respectively the coloursred, green and blue of a colour video signal, corresponding modulators40, 41 and 42 for modulating the intensity of the light bundles whichissue from the light sources 37 to 39, a plane mirror 43 and planedichroic mirrors 44 and 45 for combining into a single light bundle, themodulated light bundles and a mirror 46 for reflecting the combinedlight bundles.

[0027] The system 30 also includes an optical system, shown generally at47, for enlarging the horizontal projection angle the optical system 30being located opposite the mirror 46 and adjacent the periphery of thedisc 31, and a screen 48.

[0028] In operation, the motor 33 is arranged to rotate the disc 31 at25 revolutions per second and the component group 36 operates so that abundle of light reflected by the mirror 46 is directed through the lightguiding devices 35 as they pass successively between the mirror 46 andthe optical system 47. The spiral configuration of the light guidingdevices 35 ensures that screen 48 is scanned by 625 lines per revolutionof the disc 31 and the speed of the rotating disc 31 ensures that theimages received on the screen 48 match the number of images per secondcontained in the video signal.

[0029] Referring now to FIGS. 5 and 6 of the drawings, there is shown anembodiment of a video projection system 50 which is similar to thesystem 30 shown in FIGS. 3 and 4 and same reference numerals areincorporated in FIGS. 5 and 6 for the same components which are shown inFIGS. 3 and 4.

[0030] In the system 50, the motor 33 is located above the disc 31 andthe components of one possible embodiment of the optical system 47 areshown in detail. More particularly, the optical system 47 comprises atoroidal mirror 51, this facing away from the disc 31 and having a slot52, a concave spherical mirror 53 facing the toroidal mirror 51 and aconcave cylindrical mirror 54 facing the toroidal mirror 51.

[0031] The arrangement is such that, in operation and while disc 31rotates, a light bundle directed through the light guiding devices 35passes successively through the slot 52 to the concave mirror 53 whereit is reflected back onto the toroidal mirror 51. At the toroidal mirror51 the light bundle is reflected onto the concave cylindrical mirror 54where it is again reflected and passes under the disc 31 and is receivedat the screen 48 as a spot substantially 2.5 mm in diameter.

[0032] As each light guiding device 35 moves 0.576 degrees in front ofthe mirror 46, the light projected by each light guiding device 35 movesfrom left to right of the screen 48 along the line of the video imagecorresponding to the particular light guiding device.

[0033] In an alternative arrangement, the toroidal mirror 51 may belocated between the mirror 46 and the margin 34 of the disc 31.

[0034] Referring now to FIGS. 7 and 8 of the drawings, there is shown anembodiment of a video projection system 55 which is similar to thesystem 30 shown in FIGS. 3 and 4 and the same reference numerals areincorporated in FIGS. 7 and 8 for the same components which are shown inFIGS. 3 and 4.

[0035] In the system 55 the components of another possible embodiment ofthe optical system 47 are shown in more detail. More particularly, theoptical system comprises a plane mirror 56, this facing away from thedisc 31 and having a slot 57, a concave spherical mirror 58 facing theplane mirror 56 and the reflective surface of the plane mirror 56 beingat an angle of 45 degrees to the focal plane of the concave sphericalmirror 58, a toroidal mirror 59 being at an angle of 45 degrees toreflective light from the plane mirror 56 and a concave cylindricalmirror 60 facing the toroidal mirror 59.

[0036] The arrangement is such that, in operation, and while disc 31rotates, a light bundle directed through the light guiding devices 35passes successively through the slot 57 to the concave mirror 58, whereit is reflected back onto the plane mirror 56. At the plane mirror 56the light bundle is reflected onto the toroidal mirror 59 where it isreflected on to the concave cylindrical mirror 60 where it is againreflected and passes under the disc 31 and is received at the screen 48as a spot substantially 2.5 mm in diameter.

[0037] It will be appreciated that a video projection system inaccordance with the present invention may be adjusted to scan adifferent number of lines per image than 625. For example, if the numberof lines to be scanned is 525, the disc will be provided with acorresponding number of light guiding devices.

[0038] It will also be appreciated that, instead of providing modulatorsfor modulating the intensity of light issuing from the light sources,the light sources may be modulated by directly modulating the electricalinput currents to the light sources.

[0039] Furthermore, it will be appreciated that the term “mirror” mayinclude a block of laser reflective material, such as magnesium oxide.

1. A video projection system (30) comprising means (36, 46) forgenerating a colour light bundle coloured according to a video signaland means (31, 35) for line scanning the bundle onto a screen (48)thereby producing images on the screen (48), the system (30) alsoincluding a disc (31) adapted to rotate on an axis (32) extendingthrough a centre of the disc (31) and at right angles to the plane ofthe disc (31) characterised in that the disc (31) carries a plurality oflight guiding devices (35) extending radially of the disc (31) andspaced one from another in an angular direction in the plane of the disc(31) and each device (35) extending at an angle to the plane of the disc(31) in a corresponding plane perpendicular to the plane of the disc(31) so that each device (35) projects a corresponding one of the linesscanning a video image on to the screen (48).
 2. A video projectionsystem (30) as claimed in claim 1 characterised in that the devices (35)are arranged in a single helical configuration.
 3. A video projectionsystem (30) as claimed in claim 1 or claim 2 characterised in that thereis provided an optical system (47) for enlarging the horizontalprojection angle.
 4. A video projection system (50) as claimed in claim3 characterised in that the optical system (51, 53, 54) comprises aconcave spherical mirror (53) for reflecting the light bundle from thescanning means (31, 35), a toroidal mirror (51) for reflecting the lightbundle from the concave spherical mirror (53) and a concave cylindricalmirror (54) for reflecting the light bundle from the toroidal mirror(51) to the screen (48).
 5. A video projection system (50) as claimed inclaim 5 characterised in that the toroidal mirror (51) is provided witha slot (52) which is arranged so that the light bundle incident on theconcave spherical mirror (53) passes through the slot (52).
 6. A videoprojection system (55) as claimed in claim 4 characterised in that theoptical system (56, 57, 58, 59) comprises a concave spherical mirror(58) for reflecting the light bundle from the scanning means (31, 35), aplane mirror (56) for reflecting the light bundle from the concavespherical mirror (58), a toroidal mirror (59) for reflecting the lightbundle from the plane mirror (56) and a concave cylindrical mirror (60)for reflecting the light bundle from the toroidal mirror (59) to thescreen (48).
 7. A video projection system (55) as claimed in claim 6characterised in that the plane mirror (56) is provided with a slot (57)which is arranged so that the light bundle incident on the concavespherical mirror (58) passes through the slot (57).
 8. A videoprojection system as claimed in claim 4 or claim 5 characterised in thatthe toroidal mirror (51) is located between the light guiding devices(35) and the mirror (46).